Method for envelopment casting

ABSTRACT

A cast-bonding process includes a magnesium coating step and a magnesium nitride-forming step. The magnesium-coating step is carried out by supplying gasified magnesium into a mold in which a cast-in insert formed from an aluminum alloy, or an aluminum-based composite material is set, so that magnesium may coat the insert. The magnesium nitride-forming step is carried out by supplying nitrogen gas into the mold so that the coating magnesium and nitrogen gas may react to form magnesium nitride. Then, a molten aluminum alloy is poured into the mold for cast-bonding the insert.

TECHNICAL FIELD

[0001] This invention relates to a cast-bonding process for cast-bondingwith an aluminum alloy a cast-in insert formed from an aluminum alloy oran aluminum-based composite material.

BACKGROUND ART

[0002] The art of cast-bonding a cast-in insert formed from an aluminumalloy with an aluminum alloy is known from, for example, Japanese PatentLaid-Open Publication No. HEI-11-107848 entitled “Cylinder Liner Formedfrom a Powdered Aluminum Alloy”. This cylinder liner formed from apowdered aluminum alloy is intended for enclosing in an aluminum alloyengine block, and the cylinder liner formed from a powdered aluminumalloy and the aluminum alloy engine block are so constructed that thethermal expansibility αC of the cylinder liner and the thermalexpansibility αB of the engine block may satisfy 14×10⁻⁶/°C.≦αC≦20×10⁻⁶/° C. and 1×10⁻⁶/° C.≦αB−αC≦8×10⁻⁶/° C. Such relationshipbetween the cylinder liner and the engine block in thermal expansibilitymakes it possible to prevent the detachment of the cylinder liner fromthe engine block as it does not allow any clearance to be formed betweentheir contact surfaces.

[0003] The outer surface of the cylinder liner and the inner surface ofthe engine block are, however, merely in contact with each other, and donot react or combine with each other.

[0004] Moreover, it is likely that when a molten aluminum alloy ispoured, its surface may form an oxide film that may be caught and remainbetween it and the cylinder liner.

[0005] Moreover, the engine block increases its inside diameterconsiderably at a high temperature when the engine is in operation, butthe cylinder liner does not increase its outside diameter very much, butbecomes loose. For example, the inside diameter Di of the engine blockand the outside diameter D of the cylinder liner have a diametricalclearance S of 0.192 mm formed therebetween (S=8×10⁻⁶/° C.×300°C.×80=0.192 mm) when their relationship in thermal expansibility isexpressed as αB−αC≦8×10⁻⁶/° C., when the outside diameter of thecylinder liner and the inside diameter of the engine block are both 80mm, and when the operating temperature is 300° C. The clearance of 0.192mm brings about a loose state (JIS B 0401).

[0006] According to the related art as described above, therefore, theclearance that is likely to occur between the engine block and thecylinder liner by the oxide film formed therebetween or the temperatureof the engine in operation lowers the degree of their intimate contactdue to e.g. a decrease in the area of their mutual contact and areduction in their clamping pressure. As a result, a big difference islikely to occur to the cooling of the cylinder liners. Thus, the relatedart cannot be said to be perfect.

[0007] Therefore, there is a desire for a cast-bonding process that canform an improved bond between a cast-in insert, such as a cylinderliner, and a base material, such as an engine block.

DISCLOSURE OF THE INVENTION

[0008] According to the invention, there is provided a cast-bondingprocess characterized by comprising the cast-in insert setting step inwhich a cast-in insert formed from either an aluminum alloy or analuminum-based composite material is set in the cavity of a mold; themagnesium coating step in which magnesium is supplied into the moldhaving the cast-in insert set therein, so that the magnesium may coatthat surface of the cast-in insert which will contact a molten bath; themagnesium nitride forming step in which nitrogen gas is supplied intothe mold so as to react with the coating magnesium to form magnesiumnitride; and the cast-bonding step in which a molten aluminum alloy ispoured into the mold after nitriding to enclose the cast-in insert.

[0009] The magnesium-coating step enables the coating of the cast-ininsert with magnesium, as magnesium is supplied into the mold having thecast-in insert set therein. As a result, the following step ensures theformation of magnesium nitride on that surface of the cast-in insertwhich will contact the molten bath.

[0010] The magnesium nitride-forming step, in which nitrogen gas issupplied into the mold so as to react with the coating magnesium to formmagnesium nitride, ensures the formation of magnesium nitride on thatsurface of the cast-in insert which will contact the molten bath, andalso ensures the reduction with magnesium nitride of any oxide filmformed on the aluminum alloy surface of the cast-in insert contactingthe molten bath, or the alumina in an aluminum-based composite materialfor the cast-in insert. Magnesium nitride also serves for the reductionof any oxide film formed on the surface of the molten aluminum alloythat will be poured during the following step. As a result, it ispossible to form a strong bond between that surface of the cast-ininsert contacting the molten aluminum alloy, and the molten aluminumalloy. It is, therefore, possible to achieve an improved bonding betweenthe cast-in insert formed from an aluminum-based composite material andthe aluminum alloy.

[0011] The magnesium nitride-forming step according to the invention ispreferably carried out by preheating nitrogen gas to an appropriatetemperature outside the mold to promote the reaction of the nitrogen gaswith the coating magnesium. Alternatively, the mold is heated to anappropriate temperature to promote the reaction of magnesium. As aresult, the nitrogen gas supplied into the mold has a high temperaturethat facilitates the formation of magnesium nitride in the mold.

[0012] The heating of the mold is preferably carried out by using acartridge heater to heat it in the vicinity of the cast-in insert. Thisensures the elevation of the temperature of the nitrogen gas in thevicinity of the cast-in insert, as well as the temperature of thecast-in insert, and thereby its reaction with the magnesium coating thecast-in insert. Thus, it ensures the formation of magnesium nitride onthat surface of the cast-in insert which will contact the molten bath.Moreover, the use of a cartridge heater for heating the mold ensures theheating of any desired part of the mold to any desired temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows a casting apparatus used for carrying out acast-bonding process according to a first embodiment of the presentinvention.

[0014]FIG. 2 is a flowchart showing the cast-bonding process in whichthe casting apparatus shown in FIG. 1 is employed.

[0015]FIGS. 3A to 3D are schematic illustrations of a process formanufacturing the cast-in insert as shown in FIG. 2.

[0016]FIG. 4 is a schematic illustration of the step of setting thecast-in insert in a mold.

[0017]FIG. 5 is a schematic illustration of the step of coating theouter surface of the cast-in insert with magnesium.

[0018]FIG. 6 is a schematic illustration of the step of formingmagnesium nitride on the outer surface of the cast-in insert.

[0019]FIG. 7 is a schematic illustration of the step of cast-bonding thecast-in insert with an aluminum alloy.

[0020]FIG. 8 shows a casting made by cast-bonding the cast-in insertwith an aluminum alloy.

[0021]FIG. 9 shows a casting apparatus used for carrying out acast-bonding process according to a second embodiment of the invention.

[0022]FIG. 10 is a flowchart showing the cast-bonding process in whichthe casting apparatus shown in FIG. 9 is employed.

[0023] FIGS. 11 to 14 are schematic illustrations of the steps forcast-bonding according to the second embodiment.

[0024]FIGS. 15A and 15B are schematic illustrations of a modified formof the first embodiment.

BEST MODE OF CARRYING OUT THE INVENTION

[0025] Several preferred embodiments of the invention will now bedescribed in detail with reference to the accompanying drawings.

[0026] A casting apparatus 10 according to the first embodiment as shownin FIG. 1 includes a die casting device 11 and a gas-supplying device12. The die casting device 11 has a platform 13, and an extruder 14 anda clamping device 15 that are installed on the platform 13. The clampingdevice 15 has a mold 16.

[0027] The gas-supplying device 12 has a bottle 22 for nitrogen gas (N₂)21, a supply pipe 23 for supplying nitrogen gas 21 to the mold 16, anitrogen heating unit 24 installed in an appropriate position on thesupply pipe 23, an atmosphere oven 25, a bottle 27 for argon gas (Ar)26, a supply pipe 28 for supplying argon gas 26 to the mold 16 and apipe 29 for supplying argon gas 26 to the atmosphere oven 25. A crucible31 is installed in the atmosphere oven 25. The supply pipe 23 isequipped with a valve 32. A cast-in insert 33 is set in the mold 16. Thenitrogen-heating unit 24 has, for example, a band heater as a heatsource.

[0028] The cast-bonding process according to the first embodiment of theinvention that is carried out by employing the casting apparatus 10 willnow be described with reference to the flowchart shown in FIG. 2.

[0029] Step (hereinafter abbreviated to ST) 01: The cast-in insertformed from an aluminum-based composite material is set in the cavity ofthe mold.

[0030] ST02: Magnesium is supplied into the mold.

[0031] ST03: Nitrogen gas preheated to an appropriate temperatureoutside the mold is supplied into the mold so as to react with magnesiumto form magnesium nitride.

[0032] ST04: A molten aluminum alloy is poured to enclose the cast-ininsert formed from an aluminum-based composite material.

[0033] Steps ST01 to ST04 will now be described more specifically.

[0034]FIGS. 3A to 3D show the steps of a process for preparing a cast-ininsert according to the invention.

[0035]FIG. 3A shows a blank 34 for a cast-in insert. A cylindricalpreform 35 of porous alumina (Al₂O₃) is impregnated with a moltenaluminum alloy 36 to make an aluminum-based composite material.

[0036] Then, the blank 34 is finished to a predetermined diameter by anNC (numerically controlled) lathe 37, as shown in FIG. 3B.

[0037] The blank 34 is cast-in inserted into the container 41 of anextruding press 40, and extruded by a ram 42 through a gap between a die43 and a mandrel 44 to form a pipe 45, as shown in FIG. 3C.

[0038] The pipe 45 is cut to an appropriate length to give a cast-ininsert 33 formed from an aluminum-based composite material, as shown inFIG. 3D.

[0039]FIG. 4 shows the step of setting the cast-in insert in the mold.

[0040] Firstly, the cast-in insert 33 formed from an aluminum-basedcomposite material is set in the mold 16. The mold 16 is composed of astationary mold portion 51 and a movable mold portion 52. The movablemold portion 52 has a mold surface 53 formed therein. The stationarymold portion 51 has a mold surface 54 formed in its center, and having acast-in insert-fitting portion 55 formed thereon, and has a sidewall inwhich gas supply ports 56 and 57 are formed. Reference numeral 58denotes a cavity formed by the mold surfaces 53 and 54.

[0041] The cast-in insert 33 is fitted on the cast-in insert-fittingportion 55 of the stationary mold portion 51 of the mold 16, and then,the movable mold portion 52 is brought into tight contact with thestationary mold portion 51 as shown by arrow (1), whereby the cast-ininsert 33 is set in the cavity 58 of the mold 16.

[0042] Then, argon gas 26 is supplied into the cavity 58 of the mold 16.More specifically, the extruder 14 is brought into contact with the mold16, and argon gas 26 having an appropriate pressure is supplied into themold 16 through the argon gas supply pipe 28 as shown by arrows (2) toform an atmosphere of argon gas 26 in the cavity 58, while oxygen isdischarged from the cavity 58. The discharging of oxygen from the cavity58 is carried out by, for example, the evacuation of the cavity 58through a vacuum pump not shown, and when a certain vacuum degree hasbeen reached, the vacuum pump is stopped and argon gas 26 is supplied.

[0043]FIG. 5 shows the step of supplying argon and magnesium gases intothe mold cavity to coat the outer surface of the cast-in insert withmagnesium.

[0044] Magnesium gas 59 is supplied into the mold 16. More specifically,solid magnesium (Mg) 61 is placed in the crucible 31 in the atmosphereoven 25 shown in FIG. 1, and heated by a heating coil 62 forvaporization. No oxidation of magnesium 61 occurs, since the atmosphereoven 25 has an atmosphere of argon gas 26 supplied through the supplypipe 29.

[0045] Then, argon gas 26 is supplied through the supply pipe 29 intothe atmosphere oven 25 in which the vaporization of solid magnesium 61has occurred, so that the pressure of argon gas 26 may cause argon gas26 and magnesium gas 59 to be supplied into the mold 16 as shown byarrows (3) in FIG. 5. At the same time, the mold 16 is placed undersuction.

[0046] Thus, the magnesium coating step ensures the formation during thefollowing step of magnesium nitride on that surface 33 a of the cast-ininsert 33 which will contact a molten bath, since magnesium gas 59 issupplied into the mold 16 having the cast-in insert 33 set therein andcoats that surface 33 a of the cast-in insert 33 which will contact amolten bath.

[0047]FIG. 6 shows the step of forming magnesium nitride on the outersurface of the cast-in insert.

[0048] In continuation, nitrogen gas 21 is supplied into the mold 16.More specifically, nitrogen gas 21 leaving the bottle 22 shown in FIG. 1is heated to an appropriate temperature, such as about 400° C., in thenitrogen gas supply pipe 23 by the nitrogen heater 24, and supplied intothe mold 16 as shown by arrows (4) in FIG. 6. The heated nitrogen gas 21and magnesium gas 59 react with each other and form magnesium nitride(Mg₃N₂)63. Magnesium nitride 63 reduces any oxide film formed on thealuminum alloy surface and the alumina( Al₂O₃) 35 in the aluminum-basedcomposite material, and thereby improves the wetting property of alumina35.

[0049] The magnesium nitride-forming step, in which nitrogen gas 21 issupplied into the mold 16 so as to react with magnesium gas 59 to formmagnesium nitride 63, ensures the formation of magnesium nitride 63 onthat surface 33 a of the cast-in insert 33 which will contact the moltenbath, and also ensures the reduction with magnesium nitride 63 of anyoxide film formed on the surface 33 a of the cast-in insert contactingthe molten bath. Magnesium nitride 63 also serves for the reduction ofany oxide film formed on the surface of the molten aluminum alloy thatwill be poured during the following step. As a result, it is possible toform a strong bond between the surface 33 a of the cast-in insert 33contacting the molten aluminum alloy, and the molten aluminum alloy. Itis, therefore, possible to achieve an improved bonding between thecast-in insert 33 formed from an aluminum-based composite material, andthe aluminum alloy.

[0050] Moreover, the magnesium nitride-forming step enables nitrogen gas21 to undergo an improved reaction with the magnesium gas 59 coatingthat surface 33 a of the cast-in insert 33 which will contact the moltenbath, and facilitates the formation of magnesium nitride 63 on thesurface 33 a which will contact the molten bath, since the argon gas 21preheated to an appropriate temperature outside the mold 16 is suppliedinto the mold 16.

[0051]FIG. 7 shows the step of cast-bonding the cast-in insert with analuminum alloy.

[0052] After nitriding, a molten aluminum alloy 64 is supplied into themold 16. More specifically, the molten alloy 64 is extruded at anappropriate pressure from the cylinder 14 a of the extruder 14 as shownby an arrow (5) to fill the cavity 58, and is allowed to solidify.

[0053] Finally, the mold 16 is opened by moving the movable mold portion52 upon solidification of the molten alloy 64, and a casting 65 ascompleted is taken out. This is the end of a cast-bonding cycle in whichthe cast-in insert 33 formed from an aluminum-based composite materialis enclosed in an aluminum alloy.

[0054]FIG. 8 shows the casting 65 made by cast-bonding the cast-ininsert 33 formed from an aluminum-based composite material with thealuminum alloy. The casting 65 is not particularly limited in its use,but may, for example, provide a cylinder block for an engine made of analuminum alloy.

[0055]FIG. 9 shows a casting apparatus according to the secondembodiment of the invention. Like numerals are used to denote like partsor materials employed according to the first embodiment, and no repeateddescription thereof is made.

[0056] The casting apparatus 10 a has a gas-supplying device 12 a. Aclamping device 15 has a mold 16 a.

[0057] The gas-supplying device 12 a is a device obtained by removingthe nitrogen heater 24 from the pipe 23 in the gas-supplying device 12shown in FIG. 1, and no further description thereof is made. Accordingto a salient feature of this embodiment, the mold 16 a is heated to anappropriate temperature. More specifically, the mold 16 a has acartridge heater 66 installed in the cast-in insert-fitting portion 55 aof a stationary mold portion 51 a.

[0058]FIG. 10 shows a flowchart covering the second embodiment of theinvention.

[0059] ST11: The cast-in insert formed from an aluminum-based compositematerial is set in the cavity of the mold.

[0060] ST12: Magnesium is supplied into the mold.

[0061] ST13: Nitrogen gas is supplied into the mold and heated to anappropriate temperature by the cartridge heater in the cast-ininsert-fitting portion to form magnesium nitride.

[0062] ST14: A molten aluminum alloy is poured to enclose the cast-ininsert formed from an aluminum-based composite material.

[0063] Steps ST11 to ST14 will now be described more specifically withreference to FIGS. 11 to 14.

[0064] Firstly, the cast-in insert 33 is set in the cavity 58 of themold 16 a, as shown in FIG. 11. More specifically, the cast-in insert 33is mounted on the cast-in-insert-fitting portion 55 a of the stationarymold portion 51 a. Then, argon gas 26 is supplied into the cavity 58 ofthe mold 16 a.

[0065] Then, magnesium gas 59 is supplied into the mold 16 a as shown inFIG. 12. More specifically, magnesium gas 59 is supplied into the mold16 a with the pressure of argon gas 26, as shown by arrows (3). Themagnesium-coating step serves for the same effects with themagnesium-coating step according to the first embodiment as alreadydescribed. More specifically, it ensures the formation during thefollowing step of magnesium nitride on that surface 33 a of the cast-ininsert 33 which will contact a molten alloy, since the gasifiedmagnesium 59 coats that surface 33 a of the cast-in insert 33 which willcontact a molten alloy.

[0066] Nitrogen gas 21 is supplied into the mold 16 a as shown in FIG.13, and the mold 16 a is heated to an appropriate temperature. Morespecifically, the vicinity of the cast-in insert 33 is heated by thecartridge heater 66 installed in the cast-in insert-fitting portion 55a, so that nitrogen gas 21 may be heated to an appropriate temperature,such as about 400° C., to form magnesium nitride 63.

[0067] During the magnesium nitride-forming step according to the secondembodiment, the mold 16 a into which nitrogen gas 21 has been suppliedis heated to an appropriate temperature, whereby the nitrogen gas 21 inthe mold 16 a is heated to an appropriate temperature. As a result,nitrogen gas 21 undergoes an improved reaction with the coatingmagnesium 59 and ensures the formation of magnesium nitride 63. It ispossible to ensure the reduction of any oxide film formed on the surfaceof the aluminum alloy on the cast-in insert surface 33 a contacting themolten alloy, or the alumina in the aluminum-based composite materialfor the cast-in insert, as is the case with the first embodiment.Moreover, it is possible to reduce with magnesium nitride 63 any oxidefilm formed on the surface of the molten aluminum alloy that will bepoured during the following step. It is, therefore, possible to achievean improved bonding between the cast-in insert 33 formed from analuminum-based composite material and the aluminum alloy.

[0068] Moreover, the heating of the mold 16 a by the cartridge heater 66in the vicinity of the cast-in insert 33 ensures the reaction ofnitrogen with the magnesium 59 coating the cast-in insert 33 and thestill more effective formation of magnesium nitride 63 on that surface33 a which will contact a molten alloy.

[0069] Moreover, the use of the cartridge heater 66 for heating the mold16 a ensures the heating of any desired portion of the mold 16 a to anydesired temperature and thereby the formation of magnesium nitride 63.

[0070] After nitriding, a molten aluminum alloy 64 is supplied at anappropriate pressure to fill the mold 16 a as shown in FIG. 14, and whenthe molten alloy 64 has solidified, a casting 65 is taken out.

[0071]FIGS. 15A and 15B show a modified form of the first embodiment.Like numerals are used to denote like parts or materials as employed forthe first embodiment and no repeated description thereof is made.

[0072] The modified casting apparatus 70 shown in FIG. 15A has aclamping device 71 and a gas-supplying device 12 and the clamping device71 is equipped with a mold 72 into which a molten aluminum alloy 64 iscast directly at an atmospheric pressure.

[0073] The mold 72 has a cavity 73, a cast-in insert-supporting device74 for supporting a cast-in insert 33 b, a sprue 75 and gas supply ports76 and 77.

[0074] The modified casting process is identical to the first embodimentin the steps up to the magnesium nitride-forming step as described withreference to FIGS. 4 to 6, and those steps will be described briefly.

[0075] Firstly, the cast-in insert 33 b is set in the mold 72 andmagnesium gas 59 is supplied into the mold 72 through the gas supplyport 76 for coating the cast-in insert 33 b. Heated nitrogen gas issupplied through the gas supply port 77 so as to react with the coatingmagnesium 59 to form magnesium nitride 63. Magnesium nitride 63 reducesany oxide film formed on the aluminum alloy surface of the cast-ininsert 33 b, or alumina (A1 ₂O₃) in an aluminum-based compositematerial. These jobs are carried out after all the holes communicatingwith the cavity 73, such as the sprue 75, are closed.

[0076] Then, a molten aluminum alloy 64 is poured and when the moltenalloy 64 has solidified, the cast-in insert supporting device 74 ismoved away and a casting is taken out. FIG. 15B shows a casting 78enclosing a cast-in insert 33 b formed from an aluminum-based compositematerial.

[0077] The formation of magnesium nitride in the mold 72 according tothe modified magnesium nitride-forming step makes it possible to reduceany oxide film on the cast-in insert 33 b and on the surface of themolten aluminum alloy 64 and thereby produce an improved wettingproperty therebetween. Therefore, it is possible to achieve an improvedbonding between the cast-in insert 33 b formed from an aluminum-basedcomposite material and an aluminum alloy even if the molten aluminumalloy 64 may be cast directly into the mold 72 at an atmosphericpressure.

[0078] Although the cast-in insert 33 or 33 b has been described asbeing formed from an aluminum-based composite material, it mayalternatively be of an aluminum alloy. The cast-in insert may also be ofany desired shape.

[0079] The mold 16, 16 a or 72 is merely for illustration, and may be ofany desired construction or may have a cavity of any desired shape. Forexample, it may be a sand mold.

Industrial Applicability

[0080] This invention is particularly useful for the manufacture of anengine block having a cylinder liner, since the formation of magnesiumnitride by the reaction of nitrogen gas and magnesium after the coatingof a cast-in insert with magnesium makes it possible to achieve animproved bonding between the cast-in insert and an aluminum alloyforming a base structure.

1. A cast-bonding process, characterized by comprising the steps of: acast-in insert setting step in which a cast-in insert formed from one ofan aluminum alloy and an aluminum-based composite material is set in thea cavity of a mold; a magnesium coating step in which the an interior ofthe mold is replaced with argon gas, then magnesium is caused toevaporate inside an atmosphere oven with the cast-in insert being set inthe mold, and subsequently argon gas is supplied in the atmosphere ovento cause magnesium gas to be supplied into the mold under the pressureof the argon gas to thereby to coat with magnesium that a surface of thecast-in insert which that will contact a molten alloy; a magnesiumnitride forming step in which nitrogen gas is supplied into the mold soas to react with the coated magnesium to form magnesium nitride; and acast-bonding step in which a molten aluminum alloy is poured into themold after nitriding for cast-bonding the cast-in insert.
 2. A Thecast-bonding process according to claim 1, wherein the magnesium nitrideforming step includes heating the nitrogen gas to an appropriatetemperature outside the mold to promote the a reaction of between thenitrogen gas and the coated magnesium.
 3. A The cast-bonding processaccording to claim 1, wherein the magnesium nitride forming stepincludes heating the mold in the a vicinity of the cast-in insert to anappropriate temperature to promote the reaction between of the coatedmagnesium and the nitrogen gas.
 4. A The cast-bonding process accordingto claim 3, wherein the heating of the mold is carried out by using acartridge heater.
 5. A cast-bonding process, comprising the steps of:setting a cast-in insert into a cavity of a mold, said cast-in inserthaving a surface that will be in contact with a molten alloy and beingformed from a material selected from the group consisting of an aluminumalloy and an aluminum-based composite material; coating the surface ofsaid cast-in insert with magnesium, said surface coating including thesteps of: replacing an atmosphere within the mold cavity with argon gas;evaporating magnesium inside an atmosphere oven; and, supplying argongas to the atmosphere oven to cause magnesium gas to be supplied intothe mold under pressure of the argon gas to coat said cast-in insertsurface with magnesium; supplying nitrogen gas into said mold cavity,said nitrogen gas reacting with said magnesium coating to form amagnesium nitride coating on said cast-in insert surface; and followingforming of said magnesium nitride coating, pouring a molten aluminumalloy into said mold and allowing said aluminum alloy to solidify andthereby cast-bond the cast-in insert in the solidified aluminum alloy.6. The cast-bonding process according to claim 5, wherein the nitrogengas is heated to an appropriate temperature outside the mold to promotethe reaction between the nitrogen gas and the magnesium coating.
 7. Acast-bonding process according to claim 5, comprising the further stepof heating the mold in the vicinity of the cast-in insert to anappropriate temperature to promote the reaction between the nitrogen gasand the magnesium coating.
 8. A cast-bonding process according to claim7, wherein heating of the mold is carried out with a cartridge heater.